The present invention relates to ink jet printing processes and ink compositions suitable for said processes. More specifically, the present invention is directed to ink jet printing processes employing specific ink compositions. One embodiment of the invention resides in a thermal ink jet printing process which comprises incorporating into a thermal ink jet printing apparatus an ink composition comprising a colorant and a liquid vehicle which comprises a mixture of water and an organic component selected from the group consisting of: (1) cyclic amides of the formula ##STR1## wherein n is a number of from 2 to about 12; R is hydrogen, alkyl or substituted alkyl with from 1 to about 6 carbon atoms, a polyethoxy group of the formula EQU (--CH.sub.2 --CH.sub.2 --O).sub.m --CH.sub.2 --CH.sub.2 --OH
with m being a number of from 0 to about 9, or a polyimine group of the formula EQU (--CH.sub.2 --CH.sub.2 --NH).sub.k --CH.sub.2 --CH.sub.2 --NH.sub.2
with k being a number of from 0 to about 9; R' represents one or more substituents that can replace hydrogen in any of the hydrocarbon portions of the molecule, and is an alkyl group, a halogen atom, a sulfate group, a nitro group, a sulfone group, an amide group, or an acetyl group, wherein x is a number of from 0 to 2n+2; (2) a cyclic amide of the formula ##STR2## wherein n is a number of from 1 to about 12, R is a cyclohexyl group or a butyl group, and R' represents one or more substituents that can replace hydrogen in any of the hydrocarbon portions of the molecule, and is an alkyl group, a halogen atom, a sulfate group, a nitro group, a sulfone group, an amide group, or an acetyl group, wherein x is a number of from 0 to 2n+2; (3) cyclic esters of the formula ##STR3## wherein n is a number of from 1 to about 12, R represents one or more substituents that can replace hydrogen in any of the hydrocarbon portions of the molecule, and is an alkyl group, a halogen atom, a sulfate group, a nitro group, a sulfone group, an amide group, or an acetyl group, wherein x is a number of from 0 to 2n+2; (4) amides of the formula ##STR4## wherein R and R' are alkyl groups or substituted alkyl groups with from 2 to about 20 carbon atoms, polyethoxy groups of the formula EQU (--CH.sub.2 --CH.sub.2 --O).sub.m --CH.sub.2 --CH.sub.2 --OH
with m being a number of from 0 to about 9, or a polyimine group of the formula EQU (--CH.sub.2 --CH.sub.2 --NH).sub.k --CH.sub.2 --CH.sub.2 --NH.sub.2
with k being a number of from 0 to about 9, wherein R and R' can be bonded to each other to form a ring, and wherein R" is hydrogen or alkyl, with alkyl preferably having from 1 to about 20 carbon atoms; and mixtures thereof; and heating selected nozzles in the printing apparatus containing the ink, thereby causing droplets of the ink to be ejected in an imagewise pattern onto a substrate.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velcoity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezo electric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on open end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Known ink jet inks generally comprise a water soluble dye which is soluble in an ink vehicle such as water or a mixture comprising water and a water soluble or water miscible organic solvent. For example, U.S. Pat. No. 4,849,770 (Koike et al.) discloses an ink for use in an ink jet comprising a reactive dye or a reactive dispersing dye and a solvent composed mainly of water and an organic solvent which is not reactive with the dye. The ink is used in ink jet printing processes onto a cloth having fibers dyeable by a reactive dye, followed by a dye-fixing treatment. In addition, U.S. Pat. No. 4,793,264 (Lin et al.) discloses an ink for use with an ink jet system having material subject to corrosion by the ink, said ink comprising a fatty acid vehicle, a colorant, and amounts of anti-oxidant, preferably an alkylated hydroquinone, effective to reduce substantially the rate of corrosion on metallic parts of the system. Preferably the ink comprises an oleic acid vehicle and a vehicle additive selected from the group consisting of aromatic alcohols, aromatic ethers, dimethylsulfoxides, alkyl pyrrolidones, methoxy- and ethoxy- triglycols, aliphatic ketones, and mixtures thereof. Further Japanes Patent Publication 1-158083 discloses an ink composition for ink jet recording comprising 0.1 to 10 weight percent of a colorant, which can be either a dye or a pigment, 1 to 10 weight percent of a penetrating agent, and 25 to 09.9 weight percent of a polar solvent, such as formamide, DMSO, dimethyl ethanolamine, or N-methyl-2-pyrrolidone, having a viscosity of less than 6 mPas and a vapor pressure of less than 2 mm Hg at 20.degree. C. In addition, U.S. Pat. No. 3,994,736 (Hertz et al.) discloses a pigment-free high intensity light fast ink suitable for ink jet printing which comprises a polar solvent liquid base and a premetallized azo dye. The ink may also contain an inorganic ionizable salt to impart electrical conductivity.
Heterophase ink jet inks are also known. For example, U.S. Pat. No. 4,705,567 (Hair et al.) discloses a heterophase ink jet ink composition which comprises water and a dye covalently attached to a component selected from the group consisting of poly(ethylene glycols) and poly(ethylene imines), which component is complexed with a heteropolyanion. In addition, U.S. Pat. No. 4,597,794 (Ohta et al.) discloses an ink jet recording process which comprises forming droplets of an ink and recording on an image receiving material by using the droplets, wherein the ink is prepared by dispersing fine particles of a pigment into an aqueous dispersion medium containing a polymer having both a hydrophilic and a hydrophobic construction portion. The hydrophilic portion constitutes a polymer of monomers having mainly polymerizable vinyl groups into which hydrophilic portions such as carboxylic acid groups, sulfonic acid groups, sulfate groups, and the like are introduced. Pigment particle size may be from several microns to several hundred microns. The ink compositions disclosed may also include additives such as surfactants, salts, resins, and dyes.
While known compositions and processes are suitable for their intended purposes, a need remains for ink compositions suitable for use in ink jet printers. In addition, a need remains for ink compositions with rapid drying times. A need also remains for ink compositions that exhibit long latency times in ink jet printers. Further, there is a need for ink compositions that produce sharp, non-feathering printed characters on plain paper. There is also a need for ink compositions that enable high print quality while also providing rapid drying times and/or long latency times in ink jet printers.